1. Field of the Invention
The present invention generally relates to a magnetic pattern transferring method and a magnetic-pattern transferring device for transferring a predetermined magnetic pattern to a magnetic recording medium, such as a magnetic disk mounted on a magnetic storage device used widely as a device, such as an external storage device for a computer, and a method for manufacturing a master used in a magnetic transfer, etc., and more particularly, to a technology suitable for transferring control-signal information, such as a servo signal, an address signal, and a reproduction clock signal, data, and an OS (Operating System) to a magnetic recording medium product beforehand.
2. Description of the Related Art
In recent years, a magnetic storage device has been provided with a larger capacity and a higher recording density. Accordingly, as information has been increasing in amount, a magnetic recording medium has been desired to have a large capacity enabling a recording of a large amount of information, and to be accessible in a short time, while being available at a low cost. Realizing such a magnetic recording medium entails a use of a tracking servo technology that enables a magnetic head to scan a narrow track with high precision.
In a large-capacity magnetic recording medium, a magnetic pattern including a tracking servo signal is preformatted at a certain interval in one round of a magnetic disk. A magnetic head reads this magnetic pattern and corrects its positioning so as to run on a track with high precision.
Conventionally, such a magnetic recording medium including a predetermined magnetic pattern as mentioned above has been manufactured by recording medium by medium, and track by track, using a servo information recording device used exclusively for a magnetic recording medium. The servo information recording device requires a mechanism for positioning a recording head with high precision, and therefore is expensive. Additionally, as a magnetic recording medium has a larger capacity, recording a magnetic pattern thereon takes a longer time. Accordingly, in a process of manufacturing a large-capacity magnetic recording medium, a step of recording a magnetic pattern occupies a large proportion of the process, raising a manufacturing cost.
Under the heretofore-described circumstances, a technology replacing the above-mentioned track-by-track recording has been proposed. In this technology, a disk including a magnetic layer patterned according to a magnetic pattern is prepared as a master, and the magnetic pattern is transferred to a magnetic recording medium product via the master.
In this transferring method using the master, applying an external magnetic field to the master in contact with a magnetic recording medium to be preformatted excites the above-mentioned magnetic layer to perform a magnetic transfer. Thus, this transferring method using the master can manufacture a magnetic recording medium having a predetermined magnetic pattern in a short time, with simple manufacturing steps, and at a low cost.
As mentioned above, the master includes the magnetic layer (a soft magnetic material) patterned at a position corresponding to a predetermined magnetic pattern concerning servo information, etc. Applying the external magnetic field to this master in contact with the magnetic recording medium excites the soft magnetic material so as to transfer the magnetic-layer pattern patterned on the master to the magnetic recording medium.
Since the above-mentioned master has a fine pattern, the master is manufactured by using a lithographic technology generally used in manufacturing a semiconductor, etc. The master is manufactured by applying a photoresist on a substrate, exposing the substrate with using a photomask corresponding to a magnetic pattern, developing the magnetic pattern, etching the magnetic pattern, sputtering a soft magnetic material on the magnetic pattern, etc.
On one hand, since a semiconductor chip is considerably small, the semiconductor chip is simply discarded once the semiconductor chip has a defective pattern. On the other hand, since a magnetic recording medium has a considerably large area compared to the semiconductor chip, a defective pattern formed at one part makes the whole magnetic recording medium defective; therefore, a patterning of the magnetic recording medium is required to be controlled with higher precision so as to include no defective pattern as a whole. That is, the patterning of the magnetic recording medium requires a more precise measurement control, compared to a patterning of the semiconductor chip.
Furthermore, in order to provide a magnetic recording medium with a still higher recording density, an even finer pattern needs to be formed on the above-mentioned master with high precision. However, the above-mentioned lithographic technology has been facing a limit in forming a highly precise pattern.
FIG. 1 illustrates a conventional magnetic-pattern transferring device 100. In FIG. 1, a master 110 is placed on a magnetic recording medium 120. A predetermined magnetic field 105 is applied from a magnet 101 functioning as a magnetic field generating means. The master 110 has a magnetic layer 111 patterned according to a predetermined magnetic pattern based on a preset servo signal, etc. In a state shown in FIG. 1, the magnetic layer 111 is excited by being subjected to the magnetic field 105 so that a magnetic-layer pattern of the magnetic layer 111 is transferred to the magnetic recording medium 120 as a transferred pattern 121.
However, when the above-mentioned magnetic-layer pattern is finer, it is difficult to control a width and a depth of the magnetic layer 111 by using the contemporary lithographic technology. Therefore, the pattern of the magnetic layer 111 formed on the master 110 “deviates” subtly from the original magnetic pattern. Specifically, the pattern of the magnetic layer 111 formed on the master 110 includes a magnetically different part from the predetermined magnetic pattern. Accordingly, the magnetic recording medium 120 manufactured by a magnetic transfer using this master 110 inevitably has the transferred pattern 121 different from the original magnetic pattern.
Additionally, in the above-mentioned transferring method using the master, when applying the external magnetic field to the master in contact with the magnetic recording medium as a slave, strong and weak magnetic fields originate from the magnetic layer. Based on this phenomenon, a predetermined transferred pattern corresponding to magnetic information can be formed on the magnetic recording medium. More specifically, whereas the magnetic field becomes weaker right under the magnetic layer arranged in the master, a strong magnetic field occurs at an edge of the magnetic layer. These strong and weak magnetic fields enable a transferred pattern corresponding to original magnetic information to be formed on the magnetic recording medium.
However, since there exists a certain transition width in magnetizing the magnetic recording medium as described above, a displacement, i.e., a transfer error may occur between the edge of the magnetic layer of the master and a magnetized part formed on the magnetic recording medium.
FIG. 2 illustrates how the magnetic pattern is transferred to the magnetic recording medium 120 by using the master 110. The magnetic layer 111 is patterned on the under surface of the master 110 at a position corresponding to magnetic information to be transferred. Bringing this master 110 close to the magnetic recording medium 120 and applying the magnetic field 105 externally causes the transferred pattern 121 to be formed on the magnetic recording medium 120 between two parts of the magnetic layer 111, ideally. That is, ideally speaking, as shown in an upper illustration of FIG. 2, each of magnetized parts composing the transferred pattern 121 is formed right between edges of adjacent parts of the magnetic layer 111. Then, when an ideal transfer is performed to the magnetic recording medium 120, a waveform of a signal reproduced from the magnetic recording medium accurately reflects the original magnetic information, as shown in a lower graph of FIG. 2.
However, as mentioned above, a transfer error occurs in an actual transfer to the magnetic recording medium. FIG. 3 illustrates a case where an “extended blur” occurs in the transferred pattern 121 on the magnetic recording medium 120. When the “extended blur” occurs, an extension part 121BR extended from right under the edge of the magnetic layer 111 is formed in the transferred pattern 121 on the magnetic recording medium 120, as shown in an upper illustration of FIG. 3. Thus, when the “extended blur” occurs, a waveform of a signal reproduced from the magnetic recording medium unfavorably becomes displaced from the original magnetic information, as shown in a lower graph of FIG. 3.
Additionally, in another case contrary to the “extended blur” shown in FIG. 3, a “reduced blur”, i.e., an reduction part is formed between right under the edge of the magnetic layer 111 and the transferred pattern 121 on the magnetic recording medium 120, though not shown in the figures.
As described above, the transferred pattern being formed at a position displaced from the expected position (right under the edge of the magnetic layer 111) on the magnetic recording medium results in failure to accurately transfer necessary information to a magnetic recording medium product.